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More light spectrum info

Discussion in 'Indoor Lighting' started by smileyface, Jul 21, 2010.

  1. smileyface

    smileyface Registered+

    Hey all, I didn't write this, I got it from CannaTalk issue 4. I know we know some of this already, but it's still got other fascinating tidbits. Here's the article:

    THE INFLUENCE OF COLORS ON PLANTS - D. Kroeze MSc, CANNA Research

    The primary colors

    Researchers have traditionally distinguished seven
    colors. They are known as the colors of the rainbow,
    red, orange, yellow, green, blue, indigo and violet,
    often referred to as the primary and secondary colors.
    When put together, these primary colors create
    white light and only become visible when a ray of
    sunshine is split by a prism.
    All objects can absorb the colors within the light, reflect
    them or allow them to pass through. Science
    tells us that an object usually adopts the color it isn’t
    able to absorb itself. Because plants cannot absorb
    the color green, they must themselves be green.
    There are those who claim that light measurements
    show that plants themselves emit light particles in
    the dark and actively help create their own color.
    Just like we do, plants sense the light and colors surrounding
    them – but in a different way!

    Red light

    Plants are sensitive to the color red in the light spectrum,
    a sensitivity that arises from the plant having
    what is called a red light photoreceptor. The receptor
    is a blue-green pigment called a phytochrome
    present in the cells of a plant. You could compare
    phytochrome with an eye that only senses red
    light.
    Red light impacts a plant in many ways. Plants that
    are grown in plenty of red light are often large, but
    in general also tall with many branches. If the photoreceptor
    picks up a large quantity of natural red
    light, for example in summer when there’s plenty
    of natural red light, production of a plant hormone
    (meta-topolin) is increased. This hormone prevents
    the chlorophyll in the plant from being broken
    down, so that it stays green in spring and summer;
    advantageously, this is exactly the time that the
    plant needs its chlorophyll to convert energy coming
    from the sun into sugar. Red light also influences
    a plant’s flowering and seed formation.
    By comparing the quantity of one frequency of red
    light to the amount of another, far-red, present in
    the light, makes the plant decide whether to start
    flowering or not. The non-flowering period can be
    extended by exposing the plant to red-containing
    light during the dark period. This will, as a result,
    also extend the period of time before harvesting,
    which, of course, most growers would like to prevent.
    This also explains why it is a bad idea to enter
    the growing area when it’s dark for any time, even
    for a quick peek! The red color in light also influences
    flavor because it increases the concentration of
    special oils in plants.

    Blue light

    Plants see blue light as well as red light, using a photoreceptor
    that is called a cryptochrome. If there is
    plenty of blue light, as is the case in nature during
    autumn and winter, this receptor slows down the
    effect of a hormone called Auxin. This hormone is
    responsible for the plant’s stem and root growth.
    Auxin is also responsible for what is referred to as
    ‘apical dominance’, the phenomenon which
    causes the central stem to be dominant over side
    stems. A branch off a main stem would be dominant
    over its’ own side branches so it inhibits the
    development of axillary flowers. This causes the
    plant to create more side stems when exposed to
    bluish light and the plant stays shorter. This helps us
    to understand why plants exposed to bluish light
    are often short and bushy in appearance with a
    more robust structure. Experiments with blue light
    resulted in plants that are wider than usual. This
    can be explained by the fact that more branches
    sprout because of diminished apical dominance.
    Plants use the quantity of blue light to determine
    how far to open their stomas. The more blue light,
    the wider they open their stomas, resulting in an
    acceleration of their metabolism. High levels of
    blue light will increase metabolism, and as a consequence
    accelerate plant growth and development.
    Blue light is also responsible for leaves
    growing towards the light. Blue light avoids the multiplication
    of leaves around the fruits. A shortage of
    blue light in the spectrum will quickly cause you to
    lose 20% of your harvest. Although opinions about
    this seem to differ, the optimum red to blue light ratio
    should be 5:1 in general.
    Green light and the other colors
    Plants are hardly sensitive to green light. As far as
    we know, they lack receptors for this color.
    This is probably the case because in practice plants
    do not absorb this color. Plants which are grown
    in green light only will be exceedingly weak and
    rarely grow old.
    Clearly, plants only seem to sense those colors for
    which they have specific receptors. This is based
    on energy levels provided by each color. Plants are
    not blind but, up to a certain level, they are color
    blind. The way plants react to orange and yellow
    light is quite similar to the reaction on red light. This
    also accounts for indigo and violet which in reaction
    are similar to reactions on blue light.

    ‘Invisible’ light

    Although plants are a bit color blind, they do sense
    colors, more appropriately energy levels, that are
    entirely invisible to us humans. For example, plants
    can perceive far-red light. Plants often utilize the
    red to far-red relationship. A seed uses this relationship
    to determine whether to germinate or not.
    Plants also use that relationship to determine the
    number of other plants in the immediate surroundings.
    Because plants absorb large amounts of red
    light whilst reflecting far-red light, there will be less
    red light present in a plant’s immediate surrounding
    if other plants are in the area too. Seeds will hold
    off germinating and the plants that are already in
    place will grow faster in order to emerge above the
    other plants to acquire sufficient light for their photosynthesis.
    The fact that far-red light has the exact
    the opposite effect to that of red light makes it unsuitable
    as a light for growing. The traditional light
    bulb is a rich source of far-red light.
    Ultra violet light (UV) also influences plants. Like is
    the case with blue light, plants perceive this color
    using the cryptochrome photoreceptor. It is unclear
    whether other photoreceptors can perceive
    UV light. When increasing the quantity of UV light,
    the concentration of a purplish substance called
    Anthocyanin goes up. Anthocyanins protect plants
    against UV radiation, but also against micro-organisms
    trying to get in. The formation of Anthocyanin
    can often be seen where flaws occur such as a lack
    of oxygen. UV light not only damages the plant’s
    DNA and membranes, but immediately disrupts the
    process of photosynthesis. Therefore an excess of
    UV light is unhealthy for plants as well.

    Light is seeing

    As we have seen, light is not just essential for plants
    when it comes to supplying energy for photosynthesis.
    Although this article only reveals a small part
    of everything there is to know about light, the colors
    in it and the effects they have on plants, we did
    see how plants use colors to regulate many of their
    processes. Plants are capable of perceiving those
    colors that matter to them. Those colors give the
    plant an indication of its general environment and
    its chances of survival and reproduction. If your
    plants are to develop, grow and flower well, the
    composition of the light is at least as important as
    its quantity. Do not forget that a plant perceives
    the composition of both direct and indirect light.
    Indirect light here refers to the light that is reflected
    onto a plant by other objects such as walls or other
    plants.

    D. Kroeze, MSc.
    CANNA Research
     

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